1. Field of the Invention
Generally, the present disclosure relates to the manufacturing of semiconductor devices, and, more specifically, to various methods of forming fin isolation regions under tensile-strained fins on FinFET semiconductor devices.
2. Description of the Related Art
In modern integrated circuits, such as microprocessors, storage devices and the like, a very large number of circuit elements, especially transistors, are provided on a restricted chip area. Transistors come in a variety of shapes and forms, e.g., planar transistors, FinFET transistors, nanowire devices, etc. The transistors are typically either NMOS (NFET) or PMOS (PFET) type devices wherein the “N” and “P” designation is based upon the type of dopants used to create the source/drain regions of the devices. So-called CMOS (Complementary Metal Oxide Semiconductor) technology or products refers to integrated circuit products that are manufactured using both NMOS and PMOS transistor devices. Irrespective of the physical configuration of the transistor device, each device comprises drain and source regions and a gate electrode structure positioned above and between the source/drain regions. Upon application of an appropriate control voltage to the gate electrode, a conductive channel region forms between the drain region and the source region.
In some applications, fins for FinFET devices are formed such that the fin is vertically spaced apart from and above the substrate with an isolation material positioned between the fin and the substrate. FIG. 1A is a perspective view of an illustrative prior art FinFET semiconductor device 10 that is formed above a semiconductor substrate 12 at an intermediate point during fabrication. In this example, the FinFET device 10 includes three illustrative fins 14, an isolation material 15, a gate structure 18, sidewall spacers 20 and a gate cap layer 22. The fins 14 have a three-dimensional configuration: a height H, a width W and an axial length L. The portions of the fins 14 covered by the gate structure 18 are the channel regions of the FinFET device 10, while the portions of the fins 14 positioned laterally outside of the spacers 20 are part of the source/drain regions of the device 10. Although not depicted, the portions of the fins 14 in the source/drain regions may have additional epi semiconductor material formed thereon in either a merged or unmerged condition. FIG. 1B is a TEM photograph showing one illustrative example of a FinFET device wherein the fins 14 are vertically separated from the substrate 12 by the isolation material 15.
Device manufacturers are under constant pressure to produce integrated circuit products with increased performance and lower production costs relative to previous device generations. Thus, device designers spend a great amount of time and effort to maximize device performance while seeking ways to reduce manufacturing costs and improve manufacturing reliability. As it relates to 3D devices, device designers are currently investigating alternative semiconductor materials, such as so-called SiGe, Ge and III-V materials, to manufacture FinFET devices, which are intended to enhance the performance capabilities of such devices, e.g., to enable low-voltage operation without degrading their operating speed, by improving the mobility of the charge carriers in such devices.
However, the integration of such alternative materials on silicon substrates (the dominant substrates used in the industry) is non-trivial due to, among other issues, the large difference in lattice constants between such alternative materials and silicon. With respect to forming such lattice-mismatched materials on one another, there is a concept that is generally referred to as the “critical thickness” of a material. The term “critical thickness” generally refers to materials that are in one of three conditions, i.e., so-called “stable,” “metastable” or “relaxed-with-defects” conditions. These three conditions also generally reflect the state of the strain on the material. That is, a stable material is in a fully-strained condition that is 100% strained in at least one crystalline plane of the material.
FIG. 1C is a graph taken from an article entitled “Silicon-Germanium Strained Layer Materials in Microelectronics” by Douglas J. Paul that was published in Advanced Materials magazine (11(3), 101-204 (1999)). FIG. 1C graphically depicts these three conditions for blank (unpatterned) silicon-germanium materials (Si1-xGex; x=0-1). The vertical axis is the critical thickness in nanometers. The horizontal axis is the concentration of germanium in the silicon-germanium material. At the leftmost point on the horizontal axis is pure silicon (Ge concentration equals 0.0). At the rightmost point on the horizontal axis is pure germanium (Ge concentration equals 1.0). The two curves R and S define the stable, metastable and relaxed-with-defects regions for silicon-germanium materials having differing germanium concentration levels. Above and to the right of curve R are materials that are in the relaxed-with-defects condition. Below and to the left of the curve S are materials that are in the stable condition. The region between the two curves R and S defines the region where materials are in the metastable condition.
With reference to FIG. 1C, a layer of pure germanium (Ge concentration equal to 1.0) may be in the stable condition at a thickness up to about 1-2 nm (point CT1) and it may relax beyond about 4 nm (point CT2). Between about 2-4 nm, germanium is in a so-called “metastable condition” meaning it can easily relax if it is subjected to a relatively high temperature anneal. In contrast, a layer of silicon-germanium with a 50% concentration of germanium may be in the stable condition at thicknesses up to about 4 nm (point CT3) and it may be in a metastable condition for thicknesses between about 4-30 nm (point CT4). Above a thickness of about 30 nm, a layer of silicon-germanium with a 50% concentration of germanium will be in the relaxed-with-defects condition.
Lastly, it is known that NMOS device performance is enhanced when the channel material is tensile-strained, and that PMOS device performance is enhanced when the channel region is under a compressive strain. The problem is that, in traditional manufacturing techniques, fins for all of the devices (both N and P) are formed at the same time across the substrate so as to enable precise formation of the fins without concern for dimensional variations in the fins due to so-called etch loading effects. Thus, using prior art manufacturing techniques, the formation of fins with acceptable strain conditions for both N and P type devices is problematic.
The present disclosure is directed to various methods of forming fin isolation regions on FinFET semiconductor devices that may solve or reduce one or more of the problems identified above.